APPENDIX C - ONEBUS: PROGRAM TO COMPUTE TEST SET
SETTINGS FOR TESTING DISTANCE RELAYS
The BASIC program in this note determines voltages and currents which would appear on
distance relay terminals for ground and phase faults on a radial system with source impedance
at the same angle as line impedance. It is useful in determining test voltage and current
settings for SEL distance relays and fault locating equipment.
The program was initially designed to run on a TRS-80 Model 100 briefcase computer but
may be installed on virtually any personal computer or laptop.
The program first prompts you for the positive- and zero-sequence impedances of the trans-
mission line. Enter the data in secondary ohms for the entire length of the protected line.
Next, you may enter fault resistance, which is used in the ground-fault computations.
Enter source impedance as a per-unit value with a base of the previously-entered transmission
line data. For example, if the radial system has a source impedance of about ten percent of
the entered line impedance, enter 0.1 for the per-unit distance from the source to the bus.
Specify the distance from the bus to the fault as a fraction of the total line length. To obtain
the voltages and currents for a fault one-half the way down the line from the bus, enter 0.5
for the distance from the bus to the fault.
After you enter this data, the program begins computations. The display then shows voltages
and currents for both an AG and BC fault. These data can be entered into any active test
source.
The bottom line of the display offers you a choice of entering new impedance data (I),
changing the distance from the source to the bus (B), specifying a new fault location (F), or
quitting (Q).
Date Code 931130
Appendix C
SEL-267D/167D Instruction Manual
Appendix C-1
Summary of Contents for SEL-167D
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